In recent years, various functional characteristics have been increasingly demanded of woven and knitted fabrics and, above all, the demand for stretchability of fabrics has markedly increased. The reason for this active demand may be attributed to the fact that the elastic quality of woven and knitted clothing actively influences the delicate relationship between a comfortable feel and tightness during movement. More particularly, a marked advantage of woven and knitted clothing with good elastic quality is that no feeling of tightness arises since the elasticity allows such clothing to fit snugly, even with body action. Another unique advantage of elastic clothing is found in its crease resistant property.
Where it is desired to provide woven and knitted fabrics with stretchability, knitted fabrics can be made stretchable with comparative ease by use of ordinary false twisted yarns because of their loose structure. However, woven fabrics with satisfactory stretchability cannot be obtained by use of ordinary false twisted yarns since woven fabrics have a rigid structure as compared with knitted fabrics. However, since woven fabrics have their own excellent characteristics different from those of knitted fabrics in touch, luster, etc., it has been strongly desired to make stretch woven fabrics which preserve these characteristics inherent in woven fabrics.
Many proposals have hitherto been advanced for the enhancement of the stretchability of woven fabrics to meet the requirements mentioned above. For instance, methods have been adopted to partially introduce elastic yarns made of stretchable materials such as urethane, rubber, etc. into the fabrics. However, the use of urethane, rubber, and the like increases the cost of the fabrics and since these materials stretch too much, none of them can be used by themselves. They must be wrapped with a twisted yarn of low stretch for stretchability control. A disadvantage is then found with the use of a twisted yarn in that the production cost of the woven fabric is increased since a very inefficient and complicated process is involved in making a twisted yarn.
Several methods have been proposed to obtain a crimped yarn from a conjugate filament consisting of different polyester components.
For instance, Japanese Patent Publication No. 19108/68 discloses that a conjugate filament, which is obtained by conjugate spinning polybutylene terephthalate and polyethylene terephthalate in an eccentric sheath-core or side-by-side arrangement, can be crimped due to the potential thermal crimpability existing between the two components. However, a crimped filament prepared by simply subjecting this conjugate filament to drawing and thermal relaxation treatments can never be used to produce such a highly crimped filament that is prepared by subjecting the conjugate filament to a boiling water treatment under high load.
Also, Japanese Patent Application Laid-Open No. 84924/76 discloses a conjugate filament consisting of polybutylene terephthalate and polyethylene terephthalate, with the difference of intrinsic viscosity between the two components being defined. This conjugate filament not only fails to provide a stretch fabric with excellent elasticity but also other difficult problems arise including the development of dyeing specks due to the uneven heat setting which occurs at the time of the thermal relaxation treatment and the formation of tight picks in the woven fabric arising from high shrinkage of yarns occurring during the thermal relaxation treatment. This makes it difficult to produce stretch woven fabrics of good marketability.
Furthermore, Japanese Patent Application Laid-Open No. 67421/76 discloses a process whereby a conjugate filament made of polybutylene terephthalate and polyethylene terephthalate in a side-by-side or eccentric sheath-core arrangement is subjected to a 2-heater false twisting process. However, in this 2-heater false twisting process in which the conjugate filament is subjected to a thermal relaxation treatment after false twisting, the crimpability obtained in a boiling water treatment under high load decreases. Thus, it is impossible to obtain a crimped yarn maintaining the high crimpability which arises from a boiling water treatment under high load.